Dual Packet Configuration for Wireless Communications

ABSTRACT

A dual packet configuration for wireless communications including a first portion that is modulated according to a serial modulation and a second portion that is modulated according to a parallel modulation. The serial modulation may be DSSS whereas the parallel modulation may be OFDM. The first portion may include a header, which may further include an OFDM mode bit and a length field indicating the duration the second portion. The first portion may be in accordance with 802.11b to enable dual mode devices to coexist and communicate in the same area as standard 802.11b devices. The dual mode devices can communicate at different or higher data rates without interruption from the 802.11b devices. The packet configuration may include an OFDM signal symbol which further includes a data rate section and a data count section. In this manner, data rates the same as or similar to the 802.11a data rates may be specified between dual mode devices. The first and second portions may be based on the same or different clock fundamentals. For OFDM, the number of subcarriers, pilot tones and guard interval samples may be modified independently or in combination to achieve various embodiments. Also, data subcarriers may be discarded and replaced with pilot tones for transmission. The receiver regenerates the discarded data based on received data, such as using ECC techniques.

FIELD OF THE INVENTION

The present invention relates to wireless communications, and moreparticularly to a dual packet configuration for use in wireless localarea networks.

DESCRIPTION OF RELATED ART

The Institute of Electrical and Electronics Engineers, Inc. (IEEE)802.11 standard is a family of standards for wireless local areanetworks (WLAN) in the unlicensed 2.4 and 5 Gigahertz (GHz) bands. Thecurrent 802.11b standard defines various data rates in the 2.4 GHz band,including data rates of 1, 2, 5.5 and 11 Megabits per second (Mbps). The802.11b standard uses direct sequence spread spectrum (DSSS) with a chiprate of 11 Megahertz (MHz), which is a serial modulation technique. The802.11a standard defines different and higher data rates of 6, 12, 18,24, 36 and 54 Mbps in the 5 GHz band. It is noted that systemsimplemented according to the 802.11a and 802.11b standards areincompatible and will not work together.

A new standard is being proposed, referred to as 802.11 HRb (the “HRbproposal”), which is a high data rate extension of the 802.11b standardat 2.4 GHz. It is noted that, at the present time, the HRb proposal isonly a proposal and is not yet a completely defined standard. Severalsignificant technical challenges are presented for the new HRb proposal.It is desired that the HRb devices be able to communicate at data rateshigher than the standard 802.11b rates in the 2.4 GHz band. In someconfigurations, it is desired that the 802.11b and HRb devices be ableto coexist in the same WLAN environment or area without significantinterference or interruption from each other, regardless of whether the802.11b and HRb devices are able to communicate with each other. It mayfurther be desired that the HRb and 802.11b devices be able tocommunicate with each other, such as at any of the standard 802.11brates.

SUMMARY OF THE INVENTION

A dual packet configuration for wireless communications according to atleast one embodiment of the present invention includes a first portionthat is modulated according to a serial modulation and a second portionthat is modulated according to a parallel modulation. In one embodiment,the serial modulation is direct sequence spread spectrum (DSSS), and theparallel modulation is orthogonal frequency division multiplexing(OFDM). In further embodiments, the first portion may include a preambleand a header, where the preamble may be short or long. The header mayfurther include an OFDM mode bit indicating OFDM mode, and a lengthfield indicating the duration the second portion.

For example, the first portion may be modulated in accordance with the802.11b standard and readily received and understood by 802.11bcompatible devices operating in the 2.4 GHz frequency band. Each 802.11bdevice receives the preamble and header and determines the duration ofthe dual packet from the length field, so that the 802.11b devices knowhow long to back off during transmission of a dual mode packet. In thismanner, devices communicating with the dual mode packet configurationwill not be disrupted by the 802.11b devices, and may thus coexistwithin the same communication area as the standard 802.11b devices.

Furthermore, devices utilizing a dual mode packet configurationaccording to certain embodiments may coexist with 802.11b devices in the2.4 GHz frequency band while communicating at different or even greaterdata rates afforded by OFDM, such as data rates similar to the 802.11astandard. Whereas the 802.11b devices are currently limited to 11 Mbps,the dual mode devices may operate at 54 Mbps or higher depending uponthe particular configuration. The OFDM mode bit indicates OFDM mode toanother target OFDM device. For such OFDM embodiments, the packetconfiguration may include an OFDM synchronization pattern, an OFDMsignal symbol and an OFDM payload. The OFDM signal symbol may furtherinclude a data rate section and a data count section for specifying thedata rate the number of data bytes in the payload. In this manner, datarates the same as or similar to the 802.11a data rates may be specifiedbetween dual mode devices, such as 6, 12, 24, 36 or 54 Mbps.

In at least one embodiment, the first portion of the dual packetconfiguration may be based on a first clock fundamental whereas thesecond portion is based on a second clock fundamental. In oneembodiment, for example, the first clock fundamental is approximately 22MHz, whereas the second clock fundamental is approximately 20 MHz. The22 MHz clock signal is the clock fundamental for the 802.11b standard toenable compatibility with 802.11b devices when operating in the 2.4 GHzband. The 20 MHz clock fundamental is typical for the OFDM modulationtechnique, so that an increased data rate is achieved within the 2.4 GHzband.

In alternative embodiments, the first and second portions of the dualpacket configuration are both based on a single clock fundamental, suchas 22 MHz. Various embodiments are contemplated for the single clockfundamental. In one embodiment, each OFDM symbol includes a guardinterval with a standard number of samples for OFDM, such as 16 samplesaccording to 802.11a. Alternatively, the guard interval includes anincreased number of samples, such as 24 samples.

In yet further embodiments, each OFDM symbol in the packet configurationmay include a standard number of frequency subcarriers, such as 52frequency subcarriers according to 802.11a. Alternatively, a reducednumber of frequency subcarriers may be utilized, such as 48 subcarriers.In one embodiment, each frequency subcarrier is a data subcarrierwhereas in another embodiment, pilot tones are included. In yet anotherembodiment, each of the frequency subcarriers are initially datasubcarriers and a subset of the data subcarriers is discarded andreplaced with a corresponding number of pilot tones for transmission.Upon reception of the packet, the discarded data subcarriers arerecreated using received data, such as, for example, application oferror correction code (ECC) techniques.

A wireless communication device according to the present inventionincludes a transmitter and a receiver where each are configured tocommunicate with a dual packet configuration. The dual packetconfiguration includes first and second portions, where the firstportion is configured according to a serial modulation technique andwhere the second portion is configured according to a parallelmodulation technique. As described previously, the dual packetconfiguration may utilize DSSS modulation as the serial modulationtechnique and OFDM as the parallel modulation technique. The wirelesscommunication device may include two separate clock sources if utilizinga dual packet configuration based on first and second clockfundamentals. Alternatively, a single clock source may be utilized ifthe first and second portions are based on the same clock fundamental.The dual packet configuration utilized by the wireless communicationdevice is according to any of the various embodiments describedpreviously.

In further embodiments, the transmitter and receiver may each be capableof communicating in a super short mode in which only the second portionis utilized. The first, serial portion is not used, so that overall datathroughput may be increased. The super short mode is used only for dualmode devices and is generally not compatible with single mode devices.For example, the parallel modulation mode is not compatible with theserial modulation techniques utilized by the 802.11b devices, so that adual mode device may not coexist or communicate in the same area asactive 802.11b devices. For embodiments in which the serial modulationfor the first packet portions are 802.11b compatible, the super shortmode is advantageous when 802.11b devices are shut off or otherwise notactive in the same area, so that the dual packet mode devices may beoperated with enhanced data throughputs.

In yet a further embodiment, the transmitter and receiver may each becapable of communicating in a standard mode in which the second portionis modulated according to the serial modulation. For example, this modemay be advantageous when the serial modulation is compatible with otherdevices, such as 802.11b devices. Thus, the dual mode devices mayinclude the capability to communicate with the 802.11b devices instandard mode at the standard 802.11b rates, while also able tocommunicate with other dual mode devices at different or higher datarates.

A method of wireless communication using a dual packet configurationaccording to embodiments of the present invention includes modulating afirst portion of each packet according to a serial modulation andmodulating a second portion of each packet according to a parallelmodulation. The serial modulation may be DSSS and the parallelmodulation may be OFDM. The method may further include the various dualpacket embodiments described previously. The method may further compriseswitching to a super short mode of operation in which only the secondportion modulated according to the parallel modulation is utilized forcommunications. The super short mode enables enhanced communicationswith other dual mode devices. The method may further include switchingto a standard mode of operation in which the second portion is modulatedaccording to the serial modulation of the first portion. For 802.11bcompatible embodiments, the standard mode enables direct communicationwith 802.11b devices and enhanced communication with other dual modedevices.

A dual packet configuration for wireless communications in accordancewith embodiments of the present invention provides a suitable solutionto the 802.11 HRb proposal. Dual mode devices may be configured tocommunicate with or otherwise coexist within the same area as standard802.11b devices, while communicating with each other at different orhigher data rates.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when thefollowing detailed description of the preferred embodiment is consideredin conjunction with the following drawings, in which:

FIG. 1 is a block diagram of a WLAN system including four devicesoperating within the same room or area, where two of the devices areimplemented according to the 802.11b standard and the other two areimplemented according to the HRb proposal.

FIG. 2 is a simplified block diagram of an exemplary transceiveraccording to one embodiment of the present invention that may beutilized in either or both of the HRb devices of FIG. 1.

FIG. 3A is a graph diagram of a packet configuration utilizing a longpreamble.

FIG. 3B is a graph diagram of an alternative packet configurationutilizing a short preamble.

FIG. 4 is a graph diagram of an exemplary header, which may be used asthe header for the packet configurations of FIG. 3A or 3B.

FIG. 5 is a graph diagram of a packet configuration implementedaccording to a dual clock fundamental embodiment of the presentinvention.

FIG. 6A is a simplified block diagram of a transceiver configured toutilize the packet configuration of FIG. 5.

FIG. 6B is a simplified block diagram of an alternative transceiverconfigured to utilize the packet configuration of FIG. 5.

FIGS. 7A-7C are graph diagrams illustrating a packet configurationutilizing a single clock fundamental.

FIGS. 8A-8C are graph diagrams illustrating another exemplary packetconfiguration utilizing a single clock fundamental and a standard numberof samples in the guard interval.

FIG. 9A is a graph diagram of packet configuration utilizing 48subcarriers.

FIG. 9B is a graph diagram illustrating the subcarriers of FIG. 9Aincluding 44 data subcarriers and four pilot tones.

FIG. 9C is a graph diagram of an alternative subcarrier configurationfor the packet configuration of FIG. 9 including 48 data subcarriers.

FIGS. 10A and 10B illustrate the packet configuration of FIG. 9 in whichfour of the 48 data subcarriers are replaced with pilot tones.

FIG. 11 is a table diagram illustrating comparisons of the various OFDMembodiments illustrating variations in data rates, OFDM symbol duration,spectral width, thermal noise and delay spread spectrum as a result ofvariations in the clock rates, number of subcarriers, number of pilottones, and the number of samples in the guard interval.

FIG. 12 is a graph diagram of an exemplary packet configurationaccording a super short OFDM preamble embodiment.

DETAILED DESCRIPTION OF EMBODIMENT(S) OF THE INVENTION

FIG. 1 is a block diagram of a wireless local area network (WLAN) system100 operating within a particular room or area 101, including four WLANdevices 103, 105, 107 and 109 (103-109) are located within the area 101.The devices 103 and 105 are implemented according to at least one ofseveral embodiments of the present invention with the HRb proposal inmind, whereas the devices 107 and 109 are implemented according to the802.11b standard. All of the devices 103-109 operate in the 2.4 GHzband. The devices 103-109 may be any type of wireless communicationdevice, such as any type of computer (desktop, portable, laptop, etc.),any type of compatible telecommunication device, any type of personaldigital assistant (PDA), or any other type of network device, such asprinters, fax machines, scanners, hubs, switches, routers, etc. It isnoted that the present invention is not limited to the HRb proposal, the802.11b standard, the 802.11a standard or the 2.4 GHz frequency band,although these standards and frequencies may be utilized in certainembodiments.

The devices 107 and 109 communicate with each other at any of thestandard 802.11b rates, including 1, 2, 5.5 and 11 Mbps. The devices 103and 105 are dual mode devices that communicate with each other atdifferent or higher data rates using a dual packet configurationaccording to any one of several embodiments described below, such as thestandard 802.11a data rates of 6, 9, 12, 18, 24, 36, 48 or 54 Mbps.Alternative data rate groups are considered herein, such as a firstgroup of 6.6, 9.9, 13.2, 19.8, 26.4, 39.6, 52.8 or 59.4 Mbps, or asecond group of 5.5, 8.25, 11, 16.5, 22, 33, 44 or 49.5 Mbps, or a thirdgroup of 6.05, 9.075, 12.1, 18.15, 24.2, 36.3, 48.4 or 54.45 Mbps. Thesecond group is advantageous as including two of the 802.11b standarddata rates, namely 5.5 and 11 Mbps.

In one or more first embodiments, the dual mode devices 103-109 mayoperate or coexist in the same area 101 without significant interferencefrom each other, where the devices 103, 105 communicate with each otherat different or higher data rates than the 802.11b devices 107, 109. Inthe first embodiments, the devices 103, 105 may communicate with eachother while the devices 107, 109 may communicate with each other, butthe devices 103, 105 do not communicate with the devices 107, 109. Inone or more second embodiments, at least one of the dual mode devices103, 105 is configured with a standard mode to be able to communicatewith either of the devices 107, 109 at any one or more of the standard802.11b data rates. In at least one third embodiment, the dual modedevices 103, 105 are configured with a super short mode and communicateat different or higher data rates and are incompatible with the devices107 and 109, so that the devices 103-109 are not able to coexist withinthe same area 101. The dual mode devices 103, 105 may be implemented tooperate in the 2.4 GHz band, although other frequency bands arecontemplated.

In the first or second embodiments, it is desired that the devices 103and 105 be able to communicate with each other without interruption orinterference from either of the devices 107 and 109. This presents asignificant technical challenge since the devices 103, 105 operate atdifferent data rates when communicating with each other. The presentinvention solves this problem by enabling the devices 103 and 105 to beimplemented to be able to communicate with each other at different or athigher data rates while residing in a same area 101 as the 802.11bdevices 107, 109. Further, in the second embodiments the devices 103,105 may also communicate with either of the devices 107, 109 at the802.11b data rates

FIG. 2 is a simplified block diagram of an exemplary dual modetransceiver 200 according to one embodiment of the present inventionthat may be utilized in either or both of the devices 103, 105. Thetransceiver 200 includes an exemplary dual mode transmitter 201 andexemplary dual mode receiver 203. Within the transmitter 201, input datais provided to an encoder 211 at a particular rate of transmission. Thedata from the encoder 211 is provided to a modulator and filter 213,which modulates the encoded data onto a transmission signal asserted viaa corresponding antennae 215. The transmitted signal is received by anantennae 221 of the receiver 203, which provides the received signal toan equalizer and retrain system 223. The equalizer/retrain system 223demodulates the received signal and provides a demodulated signal to adecoder 225, which provides the output data. Within the decoder 225, asoft decision block 227 provides soft decision signals to a harddecision block 229, which formulates the final output data.

FIG. 3A is a graph diagram of a dual packet configuration 300 accordingone embodiment of the present invention utilizing a long preamble. Thepacket configuration 300 includes a long preamble 301, which may beimplemented according to the 802.11b standard having 144 bits. Alsoaccording to the 802.11b standard, the long preamble is transmitted at adata rate of 1 Mbps. The long preamble 301 is followed by a header 303,which again may be implemented according to the 802.11b standard having48 bits transmitted at a data rate of 1 Mbps. In accordance with the802.11b standard, the preamble 301 and header 303 are transmitted inapproximately 192 microseconds (μsecs). Instead of a normal 802.11bpacket however, the packet configuration 300 includes an orthogonalfrequency division multiplexing (OFDM) synchronization (sync) pattern305, followed by an OFDM signal symbol 306, followed by an OFDM payload307. OFDM is a parallel modulation technique utilizing a plurality ofsubcarrier frequencies transmitted in parallel for each of a pluralityof OFDM symbols, as further described below.

The OFDM sync pattern 305 may be implemented according to the 802.11astandard and is transmitted in approximately 16 μsecs. For example, theOFDM sync pattern 305 may be implemented according to the OFDM syncpattern specified in the 802.11a standard, which is a special patternthat enables a receiver circuit to determine precisely when the firstdata bit of the payload will arrive. The OFDM signal symbol 306 may alsobe implemented according to the 802.11a standard and is transmitted inapproximately 4 μsecs. As shown, the OFDM signal symbol 306 includes adata rate section 308 and a data count section 309. The data ratesection 308 is a bit field specifying the data rate, such as thestandard 802.11a rates, and the data count section 309 is a bit fieldindicative of the number of data bytes in the payload 307. In oneembodiment, the OFDM payload 307 is comprised of OFDM symbols at any oneof the 802.11a standard data rates of 6, 9, 12, 18, 24, 36, 48, or 54Mbps, which are PHY sublayer Service Data Units (PSDU) selectable. TheOFDM payload 307 is transmitted in “K” μsecs, where K is not necessarilydirectly related to the number of OFDM symbols in the payload portion.

FIG. 3B is a graph diagram of an alternative packet configuration 310incorporating a short preamble 311. In an embodiment in accordance with802.11b, the packet configuration 310 includes a 72-bit preamble 311transmitted at 1 Mbps, followed by a header 313 transmitted at 2 Mbps,followed by an OFDM sync pattern 315 similar to the OFDM sync pattern305, followed by an OFDM signal symbol 316 similar to the OFDM signalsymbol 306, which is followed by an OFDM payload 317 comprising OFDMsymbols at any of the standard 802.11a data rates. The data rates arePSDU selectable in a similar manner as the OFDM payload 307. Accordingto 802.11b, the short preamble 311 and the header 313 are transmitted inapproximately 96 μsecs. Again according to 802.11a, the OFDM syncpattern 315 is transmitted in 16 μsecs, the OFDM signal symbol 316 istransmitted in 4 μsecs and the OFDM payload 317 is transmitted in Kμsecs.

The short preamble 311 is utilized to reduce overhead and allow moredata to be transmitted in the same amount of time as compared to thelong preamble 301. A system utilizing the short preamble, however, mayneed a higher signal to noise (SNR) ratio to achieve accurate receptionof data. The OFDM signal symbol 316 may also include a data count anddata rate similar to the OFDM signal symbol 306 to specify the number ofinformation bytes and OFDM data rate of the payload portion.

FIG. 4 is a graph diagram of an exemplary header 400, which may be usedas the header 303 for the packet configuration 300 or the header 313 forthe packet configuration 310. The header 400 may be implemented in asimilar manner as the 802.11b standard header including an 8-bit signalfield 401, an 8-bit service field 403, a 16-bit length field 405, and a16-bit cyclical redundancy check (CRC) field 407. The header 400 ismodified, however, to include OFDM mode bit 404 within the service field403 to denote the OFDM mode of operation. The signal field 401 isnormally used to accommodate rates of up to 25.5 Mbps according to802.11b. However, if the OFDM mode is indicated by the OFDM mode bit404, then the signal field 401 is interpreted differently as any datarate supported by the transmitting device, such as either of the devices103, 105. In some embodiments, the 802.11a standard data rates are used,including 6, 9, 12, 18, 24, 36, 48, or 54 Mbps. Alternative data ratesare used in alternative embodiments, as further described below. Thelength field 405 is utilized in a similar manner as 802.11b andindicates the duration or number of μsecs for transmission of the OFDMsync pattern, signal symbol and payload, such as either of the OFDM syncpatterns 305, 315 (16 μsecs), signal symbols 306, 316 (4 μsecs) and datapayloads 307, 317 (K μsecs). For example, the length field 405 includesa bit pattern representing the number K+20 μsecs. If actual packetlength is equal to a fractional number of μsecs, then the length field405 specifies the next highest integer. For example, an actual packetlength of 237.4 μsecs would use 238 in the length field. The CRC field407 is utilized in a similar manner as the standard header for 802.11b.

In general, the dual packet configurations 300, 310 include a firstportion comprising the preamble and header and a second portioncomprising the OFDM sync, signal symbol and payload. The first portionis modulated according to serial modulation, such as direct sequencespread spectrum (DSSS) according to 802.11b, and the second portion ismodulated according to parallel modulation, such as OFDM. It isappreciated that either dual packet configuration 300 or 310 utilized byeither of the devices 103, 105, when configured according to the serialmodulation of 802.11b, are readily received and understood by either ofthe devices 107, 109. In particular, the long preamble 301 and header303 of the packet configuration 300 or the short preamble 311 and theheader 313 of the packet configuration 310, are implemented in a similarmanner and transmitted at the same data rates as those of standard802.11b devices. Regardless of whether the 802.11b devices 107, 109 areable to detect or otherwise interpret the OFDM mode bit 404 indicatingOFDM mode, the length field 405 is interpreted in the same manner as aduration of the second portion of the packet, so that both of thedevices 107, 109 are informed of the length of the OFDM sync, signalsymbol and payload of a packet transmitted by either of the devices 103,105. In this manner, any 802.11b device in the same area, such as thearea 101, as a dual mode device utilizing the dual packet configurations300 or 310 is sufficiently informed of the amount of time to back offduring transmission of a dual mode packet regardless of its data rate.

The devices 103, 105 are configured to detect the OFDM mode bit 404 inthe service field 403 and to correspondingly interpret the signal field401 to therefore identify the modulation technique and the data rate oftransmission to enable communications between the devices 103, 105. Whenthe OFDM mode is indicated, the devices 103, 105 are further configuredto detect the OFDM sync pattern, read the OFDM signal symbol, andretrieve the data in the OFDM payload. In this manner, when the devices103, 105 are utilizing the dual packet configurations 300 or 310, theymay communicate at different or higher data rates while coexistingwithin the same area 101 as any 802.11b device, such as the devices 107,109. The devices 103, 105 may further be configured with a standard modeto communicate with the devices 107, 109 at the standard 802.11b datarates if desired. For example, the devices 103, 105 may include thenecessary 802.11b communication circuitry. It is noted that the devices107, 109 are unable to understand or receive and demodulate the OFDMsync, signal symbol and payload portions of the packet configurations300 or 310 in OFDM mode. The devices 103, 105 may further be configuredto switch to a super short mode, described further below, in which onlythe second, parallel modulation portion of the packet configurations areutilized. In the super short mode, the devices 103, 105 may not coexistwith active devices 107, 109, and thus may be used when the devices 107,109 are switched off or otherwise removed from the area 101.

FIG. 5 is a graph diagram of a dual packet configuration 500 implementedaccording to a dual clock fundamental embodiment of the presentinvention. The packet configuration 500 is shown corresponding to eitherof the packet configurations 300 or 310, including a preamble 501,followed by a header 503, followed by an OFDM sync pattern 505, followedby an OFDM signal symbol 506, followed by an OFDM payload 507. Thepreamble 501 is according to either of the long or short preambles 301,311. The header 503 is implemented according to either the headers 303or 313 depending upon the rate of transmission (1 or 2 Mbps). The OFDMsync pattern 505 is implemented according to either of the OFDM syncpatterns 305 or 315. The OFDM signal symbol 506 is implemented accordingto either of the OFDM signal symbols 306 or 316, and may include datarate and data count fields in a similar manner as described for thepacket configuration 300. The OFDM payload 507 is implemented accordingto either of the OFDM payloads 307, 317.

For the packet configuration 500, the preamble 501 and the header 503comprise a first portion that is transmitted utilizing a first clockfundamental with serial modulation, whereas the OFDM sync pattern 505,the OFDM signal symbol 506 and the OFDM payload 507 comprise a secondportion that is transmitted utilizing a second clock fundamental withparallel modulation. For 802.11b, the first clock fundamental for thepreamble 501 and the header 503 is 22 Megahertz (MHz). The second clockfundamental for the OFDM sync pattern 505 and the payload 507 may beaccording to 802.11a, such as 20 MHz. In this manner, the packetconfiguration 500 is transmitted using two separate clock fundamentalsrequiring a switch in sampling rate between the header 503 and the OFDMsync pattern 505. Several embodiments are considered for providing arate change solution between the 22 and 20 MHz clock fundamentals.

FIG. 6A is a simplified block diagram of a dual mode transceiver 600configured to utilize the dual packet configuration 500. The transceiver600 includes a dual mode transmitter 601 and a dual mode receiver 603.Within the transmitter 601, the transmit signal is divided into firstand second quadrature portions which are provided to an I channeldigital-to-analog converter (DAC) 605 and to a Q channel DAC 607. The Iand Q channel DACs 605, 607 receive a clock signal from a switch 609,which receives and switched between a 40 MHz clock signal from a clocksource 613 and a 44 MHz clock signal from a clock source 611. The 40 MHzclock signal is based on the 20 MHz clock fundamental whereas the 44 MHzclock signal is based on the 22 MHz clock fundamental. The 22 MHzreceive clock and the 44 MHz transmit clock are harmonically related tothe 11 MHz 802.11b DSSS chip rate. The switch 609 is controlled by aclock mode signal to select either the 44 MHz clock signal or the 40 MHzclock signal. In this manner, the preamble 501 and the header 503 aretransmitted while the clock mode signal selects the 44 MHz clock 611whereas the OFDM sync pattern 505, signal symbol 506 and payload 507 aretransmitted utilizing the 40 MHz clock signal.

For the receiver 603, an I channel analog-to-digital (ADC) 615 and a Qchannel ADC 617 receive the respective quadrature portions of thereceived signal. A switch 619 receives the clock mode signal andcontrols or otherwise provides either a 22 MHz clock signal from a clocksource 621 or a 20 MHz clock signal from a clock source 623. Thereceiver 603 is configured to receive the preamble 501 and header 503with the 22 MHz clock signal selected, and then to receive the OFDM syncpattern 505, signal symbol 506 and payload with the 20 MHz clock signalselected. The conversion between the two clock signals may be handled invarious ways by the base band processor (BBP), such as an on-chip phaselock loop (PLL) or two external clock inputs to the BBP. The transmitter601 and the receiver 603 must each include two separate clock sourcesfor switching between the different clock fundamental signals. Further,the DACs 605, 607 and the ADCs 615, 617 must be configured to operate ateither clock fundamental. In this manner, the transceiver 600 is asomewhat complicated solution requiring additional circuitry.

FIG. 6B is a simplified block diagram of an alternative transceiver 630.The transceiver 630 includes a transmitter 631 and a correspondingreceiver 633. Here a polyphase filter is used to provide the clockchange during the OFDM portion of the signal. During the 802.11b portionof the signal, the polyphase filter is not needed, since a clock of 22or 44 MHz is already provided. During the OFDM portion of the signal,the polyphase filter is activated to rate shift the signal samplesbetween the two clock domains. The transmitter 631 operates based on a40 MHz input signal, utilizing a 40 MHz clock source 634, provided to apolyphase filter 635. The outputs of the polyphase filter 635 areprovided to an I channel DAC 637 and a Q channel DAC 639, which areoperated at a 44 MHz clock signal provided from a clock source 641. Forthe receiver 633, the receive signals are provided to an I channel ADC643 and a Q channel ADC 645. The outputs of the ADC 643, 645 areprovided to a polyphase filter 647, which asserts a 20 MHz output signalutilizing a 20 MHz clock source 651. A 22 MHz clock signal from a clocksource 649 provides the clocking signal for the ADC 643, 645. It isnoted that the transmitter 631 and the receiver 633 both utilize twoseparate clock sources. In particular, the transmitter 631 requires the40 MHz clock source 634 and the 44 MHz clock source 641, whereas thereceiver 633 utilizes the 22 MHz clock source 649 and the 20 MHz clocksource 651. Thus, additional clocking circuitry is needed and thepolyphase filter 635, 647 are rate change filters that are relativelycomplicated.

FIGS. 7A-7C are graph diagrams illustrating a dual packet configuration700 implemented according to an alternative embodiment of the presentinvention utilizing a single clock fundamental and with increasedsamples in the guard interval. As shown in FIG. 7A, the packetconfiguration 700 is similar to the packet configuration 500 andincludes a first, serially modulated portion with a preamble 701 and aheader 703, and a second parallel modulation portion including an OFDMsync pattern 705, an OFDM signal symbol 706 and a payload portion 707.The OFDM signal symbol 706 may include data rate and data count fieldsin a similar manner as described for the packet configuration 300. Thepreamble 701 is similar to the preamble 501 and may be implementedaccording to either of the preambles 301, 311 depending upon whether along or short preamble is desired. Also, the header 703 is implementedaccording either the header 303 or 313 depending upon the rate oftransmission such as either 1 or 2 Mbps. The packet configuration 700 isdifferent, however, in that the entire packet is transmitted utilizing asingle clock fundamental. In one embodiment, the clock fundamental is 22MHz according to 802.11b. Since the OFDM sync pattern 705, signal symbol706 and payload 707 are implemented utilizing OFDM, they are slightlymodified as compared to the 802.11a standard.

FIG. 7B is a graph diagram of an exemplary OFDM symbol 710 that utilizesa 22 MHz sampling fundamental according to one embodiment of the dualpacket configuration 700. The OFDM symbol 710 is similar to a standard802.11a OFDM symbol and includes a guard interval 711 followed by anInverse Fast Fourier Transform (IFFT)/FFT span 713. The OFDM symbol 710deviates from the 802.11a standard in that the cyclic extension or guardinterval 711 is comprised of 24 samples rather than the standard 16samples. The IFFT/FFT span 713 includes 64 samples similar to the802.11a standard. It is noted however that the OFDM symbol 710, whiletransmitted in 4 μsecs similar to the 802.11a standard, is based on a 22MHz sampling fundamental unlike the 802.11a standard based on 20 MHz.

FIG. 7C is a graph diagram illustrating the tone spacing of 52subcarriers 720 of the OFDM symbol 710, each subcarrier denoted Sn,where n varies from 0 to 51. The subcarriers S0-S51 include datasubcarriers and pilot tones. The frequency span 720 for each OFDM symbol710 is approximately 17 to 18 MHz (˜17.875 MHz) with a tone spacingbetween each of the 52 subcarriers of approximately 343 to 344 kilohertz(kHz) (343.75 kHz). The 52 subcarriers according to the 802.11a standardhas a frequency span of approximately 16.25 MHz with a tone spacing ofapproximately 312.5 kHz, with four (4) pilot tones. The OFDM symbol 710therefore exhibits slightly more loss as compared to a standard 802.11asymbol. A dual mode transceiver implementation configured to send andreceive the packet configuration 700 utilizing the OFDM symbol 710 doesnot require two separate clock sources or otherwise utilize two separateclock fundamentals. Instead, only a single clock fundamental, such as 22MHz, is necessary. However, a slight loss is experienced with animplementation for the packet configuration 700, such as approximately0.5 dB. Furthermore, more severe filtering is required for the packetconfiguration 700 at the single clock fundamental as compared to astandard 802.11a configuration since the overall spectrum isapproximately 10% broader. The spectral mask for the packetconfiguration 700 is also slightly harder to meet as compared to thestandard 802.11a.

FIGS. 8A-8C are graph diagrams illustrating another exemplary dualpacket configuration 800 implemented according to an alternativeembodiment utilizing a single clock fundamental and a standard number ofsamples in the guard interval. As shown in FIG. 8A, the packetconfiguration 800 is similar to the packet configuration 700, includinga preamble 801, a header 803, an OFDM sync pattern 805, an OFDM signalsymbol 806 and a payload portion 807, and is based on a single clockfundamental, such as 22 MHz, except that the 802.11a OFDM symbolwaveform is effectively unmodified. Again, the OFDM signal symbol 806may include data rate and data count fields in a similar manner asdescribed for the packet configuration 300. As shown in FIG. 8B, forexample, the guard interval 811 utilizes the 802.11a standard 16 samplesrather than the 24 samples of the guard interval 711. The OFDM symbol810 is therefore transmitted in just over 3.5 μsecs or approximately3.63637 μsecs rather than 4 μsecs.

The dual packet configuration 800 includes 52 subcarriers 820 for eachof the OFDM symbols 810, as shown in FIG. 8C. The data rates for thepacket configuration 800 is slightly modified as compared to the datarate of the packet configuration 700. In particular, the data rates forthe packet configuration 800 ranges from 6.6, 9.9, 13.2, 19.8, 26.4,39.6, 52.8, or 59.4 Mbps, which are slightly greater than the data ratesfor the packet configuration 700. The spectral width for the packetconfiguration 800 is approximately 10% wider as compared to 802.11a. Oneadvantage is that the packet configuration 800 is based on the sameclock fundamental so there is no need for clock switching or twodifferent clock generators or circuitry. Another advantage of the packetconfiguration 800 over the packet configuration 700 is that there isabout the same loss as compared to 802.11a and not the greater loss of0.5 dB as experienced for the packet configuration 700. Further, theRoot Mean Square Delay Spread Performance (RMS DS) for the packetconfiguration 800 is approximately 10% worse as compared to 802.11a.

FIG. 9A is a graph diagram of dual packet configuration 900 similar tothe dual packet configurations 700 and 800, including a first portioncomprising a preamble 901 and a header 903, and a second portionincluding an OFDM sync pattern 905, an OFDM signal symbol 906 and apayload portion 907. The dual packet configuration 900 operates with thesame or a single clock fundamental, such as 22 MHz, except that the OFDMwaveform is modified to include a reduced number of frequencysubcarriers, such as only 48 subcarriers rather than 52 subcarriers.Again, the OFDM signal symbol 906 may include data rate and data countfields in a similar manner as described for the packet configuration300. The 802.11a standard specifies a total number of subcarriers as 52which includes 48 data subcarriers and 4 pilot tones. Utilizing 48subcarriers rather than 52 generates a narrower spectrum although thespectral width is essentially the same as the 802.11a standard. Thepacket configuration 900, however, may be modified in several ways togenerate multiple embodiments of the present invention as furtherdescribed below.

FIG. 9B is a graph diagram illustrating the subcarriers 910 according toone embodiment of the dual packet configuration 900 utilizing 44 datasubcarriers and four (4) pilot tones. In this configuration, there are44 data subcarriers, denoted D0, D1, . . . D43, and 4 pilot tones,denoted P0, P1, P2 and P3. As shown in FIG. 9B, the organization of thesubcarriers 910 is a first data subcarrier D0, followed by a first pilottone P0, followed by the second data subcarrier D1, which is thenfollowed by the second pilot tone P1. Then, the data subcarriers D2 toD41 are sequentially placed in order, followed by the third pilot toneP2, the 43^(rd) data subcarrier D42, the fourth pilot tone P3, andfinally the last data subcarrier D43. The locations of the pilot tonescan vary from that shown. The figure merely illustrates one possibility.

FIG. 9C is a graph diagram of an alternative subcarrier configuration920 for the packet configuration 900 in which all 48 subcarriers aredata subcarriers, denoted D0-D47. In this embodiment, there are no pilottones, and the provided data rates are the same as that of 802.11a with24 samples in the guard interval. However, if only 16 samples areutilized in a similar manner as shown in FIG. 8B, then slightlydifferent data rates are achieved at the 22 MHz clock fundamental, whereeach respective data rate is multiplied by approximately 1.1.

FIGS. 10A and 10B illustrate yet another alternative embodiment of thesubcarrier configuration for the dual packet configuration 900 in whichfour data subcarriers are replaced with pilot tones. As shown in FIG.10A, the 48 subcarriers are all data subcarriers denoted D0-D47.However, as shown at 1001, the data subcarriers D1, D3, D44 and D46 arepunctured and discarded. As shown in FIG. 10B at 1003, the discardeddata subcarriers are replaced with four pilot tones P0, P1, P2 and P3respectively. The pilot tones are normally used to keep the phase lockloop (PLL) circuitry healthy. It is noted, however, that the PLL maytrack on the data carriers instead when no pilot tones are present. Thediscarded data is reconstructed, recreated or otherwise regenerated bythe receiver using the received data that was not discarded. The datamay be reconstructed using Error Correction Code (ECC) techniques or thelike, such as utilizing forward error correction (FEC) or the like. Thelocations of the pilot tones can vary from that shown. The figure merelyillustrates one possibility

Another variation for all of the dual packet configuration 900embodiments is to change the number of samples in the cyclic extensionor guard interval between 24 and 16 samples in a similar manner asdescribed previously for the dual packet configuration 700 and 800 asshown in FIGS. 7B and 8B. For the 48 subcarrier embodiments, changingthe number of samples in the cyclic extension from 24 to 16 changes theOFDM symbol duration from 4 μsecs to 3.63637 μsecs. Furthermore, theresulting data rates may be changed from the 802.11a and 802.11bstandards.

FIG. 11 is a table diagram illustrating comparisons of the various dualpacket configurations described heretofore illustrating variations indata rates, OFDM symbol duration, spectral width, thermal noiseperformance and delay spread performance as a result of variations inthe clock rates, number of subcarriers, number of pilot tones, and thenumber of samples in the cyclic extension or guard interval. The thermalnoise performance is measured as energy per information bit (Eb) pernoise density or strength (No) and is independent of bandwidth. Delayspread performance provides an indication of multipath-induced signaldispersion caused by echoes and reflections and is measured asroot-mean-square delay spread (RMS DS). Each of the embodiments have anembodiment number from 1 to 9, followed by reference numbersillustrating the particular packet configuration. For example,embodiment 1 is configured according to packet configuration 500,embodiment 4 is configured according to packet configuration 900 with 48data subcarriers of configuration 910 with 24 samples like configuration710, and embodiment 9 is configured according to packet configuration900 with 44 data subcarriers and data subcarrier puncture and pilot tonereplacement of configurations 1000, 1010, with 16 samples as inconfiguration 810. Embodiment 1 utilizes 2 clock fundamentals of 20 and22 MHz, whereas embodiments 2-9 utilize a single clock fundamental of 22MHz. Embodiments 1, 2 and 3 utilize 52 subcarriers, whereas embodiments4-9 utilize 48 subcarriers. Embodiments 1-4, 6, 7 and 9 utilize fourpilot tones whereas embodiments 5 and 8 utilize no pilot tones.Embodiments 1, 3, 7, 8 and 9 utilize 16 samples in the guard interval,whereas embodiments 2, 4, 5 and 6 utilize 24 samples in the guardinterval.

Embodiments 3, 7, 8 and 9 result in slightly modified OFDM symbolduration of approximately 3.64 μsecs. The spectral width for embodiment1 is the same as that as 802.11a standard. Embodiments 2 and 3 exhibit10% wider spectral width than 802.11a whereas embodiments 4-9 exhibit0.83% wider spectral width than 802.11a. The thermal noise performancefor embodiments 1, 3, 7 and 8 are approximately the same as that of802.11a, whereas embodiments 2, 4-6 and 9 exhibit slightly worse noiseperformance than 802.11a. The delay spread performance for embodiment 1is the same as that as 802.11a. Embodiments 2, 4, 5, and 6 exhibit 50%better delay spread performance as compared to 802.11a, whereasembodiments 3, 7, 8 and 9 exhibit 10% worse delay spread performance ascompared to 802.11a.

FIG. 12 is a graph diagram of an exemplary packet configuration 1200according a super short mode of operation. In general, the first,serially modulated packet portions are dropped for the super short mode.In the embodiment shown, the packet configuration 1200 includes an OFDMsync pattern 1201, followed by an OFDM signal symbol 1203, followed byan OFDM payload 1205. It is understood that other parallel modulationtechniques may be utilized. A data rate section 1207 and a data countsection 1209 are provided in the signal symbol 1203. The data ratesection 1207 is a bit field specifying the data rate, such as thestandard 802.11a rates, and the data count section 1209 is a bit fieldindicative of the number of data bytes in the payload 1205. The packetconfiguration 1200 does not include a standard 802.11b header and istherefore incompatible and not otherwise interoperable or coexistentwith 802.11b devices. The entire packet configuration 1200 utilizes asingle clock source, such as 20 MHz, to simplify the transceivercircuitry. The packet configuration 1200 may be utilized by either ofthe devices 103, 105 within the area 101 to communicate with each other.However, the standard 802.11b devices 107, 109 are not compatible andmay not coexist within the same area 101 as the devices 103, 105utilizing the super short preamble option.

It is appreciated that a dual packet configuration for wirelesscommunications according to at least one embodiment of the presentinvention enables compatibility with existing devices based on a serialmodulation while enabling communication at different or higher datarates by using parallel modulation for the payload. In particular, thedual packet configuration includes a first portion that is modulatedaccording to a serial modulation and a second portion that is modulatedaccording to a parallel modulation. A dual packet configuration with afirst portion comprising a preamble and header modulated with DSSSserial modulation according to 802.11b in the 2.4 GHz band enables dualmode devices to coexist in the same communication area as 802.11bcompatible devices. The header includes a length field that specifiesthe duration of the second portion of the dual packet, so that 802.11bdevices know how long to back off. The second portion modulated with aparallel modulation, such as OFDM or the like, enables the dual modedevices to communicate at different or higher rates, such as up to 54Mbps or more, without interruption from the 802.11b devices.

In some embodiments, dual mode transmitters and receivers may each becapable of communicating in a super short mode in which only the secondportion is utilized. The first, serial portion is not used, so thatoverall data throughput may be increased.

The super short mode is used only for dual mode devices and is generallynot compatible with single mode devices. For example, the parallelmodulation mode is not compatible with the serial modulation techniquesutilized by the 802.11b devices, so that a dual mode device may notcoexist or communicate in the same area as active 802.11b devices. Forembodiments in which the serial modulation for the first packet portionsare 802.11b compatible, the super short mode is advantageous when802.11b devices are shut off or otherwise not active in the same area,so that the dual packet mode devices may be operated with enhanced datathroughputs.

In other embodiments, the dual mode transmitters and receivers may eachbe capable of communicating in a standard mode in which the secondportion is modulated according to the serial modulation. For example,this mode may be advantageous when the serial modulation is compatiblewith other devices, such as 802.11b devices. Thus, the dual mode devicesmay include the capability to communicate with the 802.11b devices instandard mode at the standard 802.11b rates, while also able tocommunicate with other dual mode devices at different or higher datarates.

Although a system and method according to the present invention has beendescribed in connection with the preferred embodiment, it is notintended to be limited to the specific form set forth herein, but on thecontrary, it is intended to cover such alternatives, modifications, andequivalents, as can be reasonably included within the spirit and scopeof the invention as defined by the appended claims.

1. A transmitter that uses a dual packet configuration for wirelesscommunication, comprising: a first modulator that modulates a firstportion of each packet solely according to a serial modulation; and asecond modulation that modulates second portion of each packet accordingto a parallel modulation.
 2. (canceled)
 3. The transmitter of claim 1,wherein the first portion includes a preamble and a header.
 4. Thetransmitter of claim 3, wherein the preamble comprises a long preamble.5. The transmitter of claim 3, wherein the preamble comprises a shortpreamble.
 6. The transmitter of claim 3, the header including an OFDMmode bit.
 7. The transmitter of claim 6, the header further including alength field indicating the duration the second portion.
 8. Thetransmitter of claim 1, the second portion further comprising: an OFDMsynchronization pattern; an OFDM signal symbol, the OFDM signal symbolincluding a data rate section and a data count section; and an OFDMpayload.
 9. The transmitter of claim 8, further comprising: the OFDMsignal symbol including a data rate section and a data count section.10. The dual packet configuration of claim 1, further comprising: thefirst portion based on a first clock fundamental; and the second portionbased on a second clock fundamental.
 11. The transmitter of claim 10,wherein the first clock fundamental is approximately 22 Megahertz (MHz)and the second clock fundamental is approximately 20 MHz.
 12. Thetransmitter of claim 1, wherein the first and second portions are basedon a single clock fundamental.
 13. The transmitter of claim 12, thesecond portion including OFDM symbols wherein each OFDM symbol includesa guard interval with a standard number of samples for OFDM.
 14. Thetransmitter of claim 12, the second portion including OFDM symbolswherein each OFDM symbol includes a guard interval with an increasednumber of samples.
 15. The transmitter of claim 12, the second portionincluding OFDM symbols wherein each OFDM symbol includes a reducednumber of frequency subcarriers.
 16. The transmitter of claim 15,wherein each OFDM symbol includes 48 frequency subcarriers.
 17. Thetransmitter of claim 15, wherein each of the frequency subcarriers is adata subcarrier.
 18. The transmitter of claim 15, wherein the frequencysubcarriers include at least one pilot tone.
 19. The transmitter ofclaim 15, wherein each of the frequency subcarriers initially comprisesa data subcarrier the second modulator discards a subset of the datasubcarriers and replaces the discarded data subcarriers with acorresponding number of pilot tones for transmission.
 20. A wirelesscommunication device that is configured to communicate using a dual packconfiguration, comprising: a transmitter configured to transmit packetswith a dual configuration; a receiver configured to receive packets witha dual configuration; and the dual packet configuration including firstand second portions, the first portion modulated solely according to aserial modulation method and the second portion modulated according to aparallel modulation method.
 21. (canceled)
 22. The wirelesscommunication device of claim 20, the first portion including a headerwith an OFDM mode bit.
 23. The wireless communication device of claim22, the header further including a length field indicating the durationof the second portion.
 24. The wireless communication device of claim20, further comprising: a first clock source based on a first clockfundamental, the first portion based on the first clock fundamental; anda second clock source based on a second clock fundamental, the secondportion based on the second clock fundamental.
 25. The wirelesscommunication device of claim 24, wherein the first clock fundamental isapproximately 22 Megahertz (MHz) and the second clock fundamental isapproximately 20 MHz.
 26. The wireless communication device of claim 20,further comprising; a clock source based on a clock fundamental, thefirst and second portions based on the clock fundamental.
 27. Thewireless communication device of claim 26, wherein the second portionincludes OFDM symbols, each OFDM symbol including a guard interval witha standard number of samples for OFDM.
 28. The wireless communicationdevice of claim 26, wherein the second portion includes OFDM symbols,each OFDM symbol including a guard interval with an increased number ofsamples.
 29. The wireless communication device of claim 26, wherein thesecond portion includes OFDM symbols, each OFDM symbol including areduced number of frequency subcarriers.
 30. The wireless communicationdevice of claim 29, wherein each of the frequency subcarriers is a datasubcarrier.
 31. The wireless communication device of claim 29, whereinthe frequency subcarriers include at least one pilot tone.
 32. Thewireless communication device of claim 29, further comprising: thetransmitter discarding at least one of the data subcarriers andreplacing the discarded data subcarriers with a corresponding number ofpilot tones; and the receiver regenerating the discarded datasubcarriers based on received data subcarriers.
 33. The wirelesscommunication device of claim 20, wherein the transmitter and receiverare each capable of communicating in a super short mode in which onlythe second portion modulated according to the parallel modulation isutilized.
 34. The wireless communication device of claim 20, wherein thetransmitter and receiver are each capable of communicating in a standardmode in which the second portion is modulated according to the serialmodulation.
 35. The wireless communication device of claim 20, furthercomprising: the transmitter and receiver each configured to operate inthe 2.4 Gigahertz frequency band.
 36. A method of wireless communicationusing a dual packet configuration, comprising: modulating a firstportion of each packet solely according to a serial modulation; andmodulating a second portion of each packet according to a parallelmodulations wherein modulating the second portion of each packetcomprises modulating the second portion according to orthogonalfrequency division multiplexing (OFDM).
 37. (canceled)
 38. The method ofclaim 36, further comprising: including a header with an OFDM mode bitin the first portion; and including a length field in the headerindicating a duration of the second portion.
 39. The method of claim 36,wherein modulating the first portion of each packet comprises modulatingbased on a first clock fundamental, and wherein modulating the secondportion of each packet comprises modulating based on a second clockfundamental.
 40. The method of claim 36, wherein modulating the firstand second portions of each packet comprises modulating based on asingle clock fundamental.
 41. The method of claim 40, wherein modulatingthe second portion of each packet comprises including a guard intervalwith a standard number of samples for each OFDM symbol.
 42. The methodof claim 40, wherein modulating the second portion of each packetcomprises including a guard interval with an increased number of samplesfor each OFDM symbol.
 43. The method of claim 40, wherein modulating thesecond portion of each packet comprises including a reduced number offrequency subcarriers for each OFDM symbol.
 44. The method of claim 43,further comprising: discarding a subset of the data subcarriers;replacing the discarded data subcarriers with a corresponding number ofpilot tones for transmission; and regenerating the discarded datasubcarriers based on received data.
 45. The method of claim 36, furthercomprising: switching to a super short mode of operation in which onlythe second portion modulated according to the parallel modulation isutilized for communications.
 46. The method of claim 36, furthercomprising: switching to a standard mode of operation in which thesecond portion is modulated according to the serial modulation.
 47. Thetransmitter according to claim 1, wherein the serial modulationcomprises direct sequence spread spectrum (DSSS).
 48. The wirelesscommunication device according to claim 20, wherein the serialmodulation is direct sequence spread spectrum (DSSS).
 49. The method ofclaim 36, wherein modulating a first portion of each packet comprisesmodulating according to direct sequence spread spectrum (DSSS).